Immunogenicity and safety of measles vaccine in ill African children

Health effects of utilising hospital contacts to provide measles vaccination to children 9-59 months-a randomised controlled trial in Guinea-Bissau

BACKGROUND

Measles vaccination coverage in Guinea-Bissau is low; fewer than 80% of children are currently measles vaccinated before 12 months of age. The low coverage hampers control of measles. Furthermore, accumulating evidence indicates that measles vaccine has beneficial non-specific effects, strengthening the resistance towards other infections. Thus, even if children are not exposed to measles virus, measles-unvaccinated children may be worse off. To increase vaccination coverage, WHO recommends that contacts with the health system for mild illness are utilised to vaccinate. Currently, in Guinea-Bissau, curative health system contacts are not utilised.

METHODS

Bandim Health Project registers out-patient consultations and admissions at the paediatric ward of the National Hospital in Guinea-Bissau. Measles-unvaccinated children aged 9-59 months consulting for milder illness or being discharged from the paediatric ward will be invited to participate in a randomised trial. Among 5400 children, randomised 1:1 to receive standard measles vaccine or a saline placebo, we will test the hypothesis that providing a measles vaccine at discharge lowers the risk of admission/mortality (composite outcome) during the subsequent 6 months by 25%. All enrolled children are followed through the Bandim Health Project registration system and through telephone follow-up. The first 1000 enrolled children are furthermore followed through interviews on days 2, 4, 7 and 14 after enrolment.

DISCUSSION

Utilising missed vaccination opportunities can increase vaccination coverage and may improve child health. However, without further evidence for the safety and potential benefits of measles vaccination, these curative contacts are unlikely to be used for vaccination in Guinea-Bissau.

TRIAL REGISTRATION

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Factors That Influence the Immune Response to Vaccination

There is substantial variation between individuals in the immune response to vaccination. In this review, we provide an overview of the plethora of studies that have investigated factors that influence humoral and cellular vaccine responses in humans. These include intrinsic host factors (such as age, sex, genetics, and comorbidities), perinatal factors (such as gestational age, birth weight, feeding method, and maternal factors), and extrinsic factors (such as preexisting immunity, microbiota, infections, and antibiotics). Further, environmental factors (such as geographic location, season, family size, and toxins), behavioral factors (such as smoking, alcohol consumption, exercise, and sleep), and nutritional factors (such as body mass index, micronutrients, and enteropathy) also influence how individuals respond to vaccines. Moreover, vaccine factors (such as vaccine type, product, adjuvant, and dose) and administration factors (schedule, site, route, time of vaccination, and coadministered vaccines and other drugs) are also important. An understanding of all these factors and their impacts in the design of vaccine studies and decisions on vaccination schedules offers ways to improve vaccine immunogenicity and efficacy.

General practitioners and vaccination of children presenting with a benign infection

PURPOSE

To assess the self-reported vaccination behavior of general practitioners (GPs) when asked whether they would recommend the vaccination of a child presenting with a febrile uncomplicated common cold.

METHODS

We performed a cross-sectional survey in 2014 on a national sample of GPs. GPs were randomly assigned to one of eight clinical vignettes, all describing a child presenting with an uncomplicated febrile common cold, but differing by age (4 or 11 months), temperature (38°C or 39°C), and the mother's emotional state (calm or worried). GPs were asked whether they would recommend immediate vaccination of the child with a hexavalent vaccine (diphtheria, tetanus, pertussis, poliomyelitis, Haemophilus influenzae type b, and hepatitis B), or postpone it. We investigated the relation between the GPs' recommendation to vaccinate, the clinical vignette's variables, and the GPs' perceptions, attitudes, and practices toward vaccination in a multivariate model.

RESULTS

Among the 1582 participating GPs, 6% recommended immediate vaccination. This behavior was more frequent with a temperature of 38°C rather than 39°C (10% vs. 3%, P<0.001). GPs who felt comfortable giving explanations about vaccine safety were more likely to recommend immediate vaccination of the febrile child (P=0.045), but none of the other GPs' characteristics were associated with their vaccination behavior.

CONCLUSIONS

Almost all GPs postponed the hexavalent vaccination of the febrile child presenting with an uncomplicated viral disease; fever being the major factor affecting their decision. More research is needed on vaccination responses in sick children, as well as clearer guidelines.

Assessing the cost-effectiveness of different measles vaccination strategies for children in the Democratic Republic of Congo

INTRODUCTION

One of the goals of the Global Measles and Rubella Strategic Plan is the reduction in global measles mortality, with high measles vaccination coverage as one of its core components. While measles mortality has been reduced more than 79%, the disease remains a major cause of childhood vaccine preventable disease burden globally. Measles immunization requires a two-dose schedule and only countries with strong, stable immunization programs can rely on routine services to deliver the second dose. In the Democratic Republic of Congo (DRC), weak health infrastructure and lack of provision of the second dose of measles vaccine necessitates the use of supplementary immunization activities (SIAs) to administer the second dose.

METHODS

We modeled three vaccination strategies using an age-structured SIR (Susceptible-Infectious-Recovered) model to simulate natural measles dynamics along with the effect of immunization. We compared the cost-effectiveness of two different strategies for the second dose of Measles Containing Vaccine (MCV) to one dose of MCV through routine immunization services over a 15-year time period for a hypothetical birth cohort of 3 million children.

RESULTS

Compared to strategy 1 (MCV1 only), strategy 2 (MCV2 by SIA) would prevent a total of 5,808,750 measles cases, 156,836 measles-related deaths and save U.S. $199 million. Compared to strategy 1, strategy 3 (MCV2 by RI) would prevent a total of 13,232,250 measles cases, 166,475 measles-related deaths and save U.S. $408 million.

DISCUSSION

Vaccination recommendations should be tailored to each country, offering a framework where countries can adapt to local epidemiological and economical circumstances in the context of other health priorities. Our results reflect the synergistic effect of two doses of MCV and demonstrate that the most cost-effective approach to measles vaccination in DRC is to incorporate the second dose of MCV in the RI schedule provided that high enough coverage can be achieved.

Immunological considerations regarding parental concerns on pediatric immunizations

Despite the fundamental role of vaccines in the decline of infant mortality, parents may decide to decline vaccination for their own children. Many factors may influence this decision, such as the belief that the infant immune system is weakened by vaccines, and concerns have been raised about the number of vaccines and the early age at which they are administered. Studies focused on the infant immune system and its reaction to immunizations, summarized in this review, show that vaccines can overcome those suboptimal features of infant immune system that render them more at risk of infections and of their severe manifestations. In addition, many vaccines have been shown to improve heterologous innate and adaptive immunity resulting in lower mortality rates for fully vaccinated children. Thus, multiple vaccinations are necessary and not dangerous, as infants can respond to several antigens as well as when responding to single stimuli. Current immunization schedules have been developed and tested to avoid vaccine interference, improve benefits and reduce side effects compared to single administrations. The infant immune system is therefore capable, early after birth, of managing several antigenic challenges and exploits them to prompt its development.

Immune response to measles vaccine in primary school students

This cross sectional study was performed to estimate the prevalence of serological evidence of immunity to Measles in primary school students (age 6-12) that have a history of twice vaccination against measles, on 9 and 15 month old and determining the appropriate age to re-vaccination. Multistage sampling was used to select students to participate in the present study. Immunization status and documentary evidence of immunization was recorded from the Personal Health Record. Measles antibodies were measured using enzyme-linked immunosorbent assay (ELISA). Sufficient blood for antibody testing was obtained from 1665 children, 975 (57%) were girls and 720 (43%) were boys, respectively and mean age was 9.17 +/- 1.53 years. On the whole, 1198 subjects (72%) were seropositive and 467 (28%) were seronegative at all. Among girls and boys, 72 and 71%, were seropositive respectively. These differences were not statistically significant between the two sexes (p = 0.404). Antimeasles antibody titer decreased with increasing age from 6 to 10 years old, (76.5% in 6 years old group vs. 71% in 10 years old group) and then rise to 78% in 11-12 years old group. These differences were not statistically significant between age groups (p = 0.775). the immunity produced by the measles vaccine is not enough. Decrease of protective effect of measles vaccine, suggests the necessary of preschool revaccination.

Immunogenicity of measles and rubella vaccines in Oman: a prospective clinical trial

A prospective immunogenicity trial of measles and rubella vaccines was conducted in Oman. Children received measles vaccine at age 9 months and measles-rubella vaccine at age 15 months. Serum specimens were tested for measles-specific IgG and rubella-specific IgG. Of 1025 eligible infants, 881 (86.0%) returned for all five visits and had adequate serum samples for testing. Seroconversion to measles after vaccination at 9 months was 98.1%. At 15 months, 47 (5.3%) of the 881 children were seronegative for measles; of these, 44 (93.6%) seroconverted. At 16 months, 99% of the children seronegative at age 9 months seroconverted after receiving two doses of measles vaccine. At age 15 months, 684 (77.6%) children were seronegative for rubella. Of these, 676 (98.8%) seroconverted by age 16 months. One dose of measles vaccine at age 9 months was highly immunogenic. One dose of measles-rubella vaccine at age 15 months closed the remaining measles immunogenicity gap and resulted in a high rate of rubella seroconversion.

Addressing parents' concerns: do multiple vaccines overwhelm or weaken the infant's immune system?

Recent surveys found that an increasing number of parents are concerned that infants receive too many vaccines. Implicit in this concern is that the infant's immune system is inadequately developed to handle vaccines safely or that multiple vaccines may overwhelm the immune system. In this review, we will examine the following: 1) the ontogeny of the active immune response and the ability of neonates and young infants to respond to vaccines; 2) the theoretic capacity of an infant's immune system; 3) data that demonstrate that mild or moderate illness does not interfere with an infant's ability to generate protective immune responses to vaccines; 4) how infants respond to vaccines given in combination compared with the same vaccines given separately; 5) data showing that vaccinated children are not more likely to develop infections with other pathogens than unvaccinated children; and 6) the fact that infants actually encounter fewer antigens in vaccines today than they did 40 or 100 years ago.

Mild illness at or after measles vaccination does not reduce seroresponse in young children

We analyzed data from a randomized trial of AIK-C, high-titre (EZ-H) or medium-titre EZ (EZ-M) vaccines in 3.5 and 6 month old infants in Kinshasa, Zaire, in which the occurrence of rhinorrhoea, cough, diarrhoea, fever, conjunctivitis or rash was monitored for 15 days post-vaccination (including the day of vaccination, day 0). We compared sero-response at 6 weeks and 6 months post-vaccination among children with and without mild illness at or after vaccination. Seroresponse tended to be higher in children with mild illness after vaccination than those without, whether days 0-7 or 8-15 were examined. For most symptoms, these differences did not reach statistical significance after adjusting for prevaccination maternal antibody level. However, in the EZ-M group, the proportion of children attaining at least the median post-vaccination antibody level was significantly higher in children with rhinorrhoea in days 0-7 post-vaccination than those without (adjusted odds ratio 2.6, 95% CI 1.08-6.27), as was that among children with at least one symptom in days 0-7 compared with children with no symptoms (adjusted OR 4.55, 95% CI 1.18-17.57). There were no significant differences in post-vaccination antibody levels among children with symptoms compared either to those without the specific symptom or those with no symptoms. Fever on the day of vaccination or at home visits on 7, 10 or 14 days post-vaccination, did not affect seroconversion or GMTs. Regression models showed no relation between the cumulative number of days with symptoms and antibody increase after vaccination. Analysis of antibody levels at 6 months post-vaccination showed no consistent differences according to presence or absence of symptoms. These findings provide further strong support to recommendations that mild illness is not a reason to delay measles vaccination.

Adverse impact of infections on antibody responses to measles vaccination

Antibody titres were determined in 102 Thai infants who were vaccinated at 9-months of age during the respiratory disease season. The symptom densities of illnesses at or following vaccination, including rhinorrhea and diarrhea, were significantly lower among seroconverters, although the simple presence or absence of specific symptoms was not significantly related to seroconversions. Logistic regression indicated that neutralization test antibody titres below the median titre of 1:80 following vaccination were significantly more frequent among those with rhinorrhea when vaccinated and among those with diarrhea after vaccination. Compared with a referent group without these symptoms, titres were lower in those who had rhinorrhea when vaccinated, rhinorrhea during the first week post vaccination, and diarrhea in either of the two follow-up weeks. Illnesses concurrent or subsequent to measles vaccination adversely affected antibody responses in these study objects.

Serologic response to measles-mumps-rubella vaccine among children with upper respiratory tract infection

The influence of concurrent upper respiratory tract infection (URTI) on immune response to MMR (measles, mumps, rubella) vaccine was evaluated by measuring IgG levels for each viral component immediately before vaccination and 6 months after vaccination in 198 12-month-old children (101 children without URTI and 97 with URTI at time of vaccination). None of the children had antibodies to measles, mumps or rubella before vaccination. Seroconversion rates and the geometric means of the antibody titers in children without URTI and in children with URTI at the time of vaccination were similar. MMR vaccination should not be delayed in children with such infections.

Immunogenicity of measles vaccine from a hospital based and outreach programme in rural Kenya

Data on efficacy of rural immunization programmes are scarce. We investigated the seroconversion rate following measles vaccination in an outreach programme in Kakamega District, Kenya. Of 170 children, 120 (71%) showed seroconversion after vaccination. Haemagglutination inhibition test was performed on paired blood samples before and 30 days or more (mean 46, range 30-70 days) after vaccination. These results are comparable to results found by other studies in developing countries. Geometrical mean titres before vaccination of children in the age group above 14 months were significantly lower than in the younger age groups (P less than 0.001). This investigation indicates that seroconversion rate studies are feasible in remote rural areas.

Serological response to measles revaccination in a highly immunized military dependent adolescent population

In the spring of 1986, there was a measles outbreak in the city of El Paso, Texas, with 92 cases reported to the City-County Health Department. Of those 92 cases, 31 (32%) occurred within a public high school's student population of 2524. A mass measles vaccination program was undertaken at that high school in order to limit the outbreak. The student enrollment included a military dependent population of 368 students. Despite documented histories of prior measles immunizations in this military dependent subgroup, three individuals contracted the disease. Since this subgroup of students represented a highly immunized adolescent population, it was of interest to serologically determine their immune status prior to and following reimmunization with the expectation that such a study would provide information relating to the level of "protective" immunity. Prevaccination and postvaccination sera were obtained from 95 students. Results of measuring anti-measles antibody activity by ELISA indicate that 13 (14%) students responded to revaccination and experienced a fourfold or greater rise in IgG antibody levels. There were no detectable IgM responses. All of the students who responded to revaccination produced an anamnestic response (IgG boost only). Since most of these individuals had received first immunizations at 15 months of age or older, these findings suggest that secondary vaccine failure (waning immunity) was responsible for the putative "lowered" immunity in these individuals, instead of primary vaccine failure (maternal antibody suppression). These findings support current recommendations for measles booster revaccination of school-age children and adolescents.